1. Field of the Invention
The present invention relates to a film for use in heat/pressure bond print lamination, having superior gloss and provided with a heat-adhesive layer which enables lamination to a printed paper, for example, simply by the application of heat and pressure without requiring any adhesive.
2. Description of Related Art
It is a known technique to cover a printed paper such as a printed art paper with a film for the purpose of protecting the print, imparting resistance to water and oil and providing gloss. This technique is referred to as "print lamination" in the field of technology concerned.
Hitherto, the print lamination is carried out by a method called dry lamination in which, in a coating section of a laminator, an adhesive dissolved in an organic solvent is applied to a plastic film which is used as a substrate, and the organic solvent is evaporated in a dryer oven, the surface of the substrate carrying adhesive thereon being then bonded to the printed paper under the application of heat and pressure.
The dry lamination method suffers from a disadvantage in that the thickness of the adhesive layer is small because the adhesive is dissolved in an organic solvent, so that undulation of the printed paper is directly reflected to impair the gloss. In addition, this method cannot provide sufficiently high adhesive strength.
In recent years, films for print lamination are available, which themselves have bondability so as to be bonded by heat and pressure without the aid of any adhesive.
For example, Japanese Unexamined Patent Publication (Tokkai-sho) No. 56-42652 discloses a film for print lamination which comprises a biaxially drawn polypropylene film having a heat-adhesive layer provided on one side thereof, said heat-adhesive layer comprising an ethylene vinyl acetate copolymer.
Japanese Examined Patent Publication (Tokko-sho) No. 63-12792 discloses a film for print lamination comprising a biaxially drawn polypropylene film layer and a heat-adhesive layer which comprising polyethylene or an ethylene copolymer such as a copolymer of ethylene and propylene, butene-1, vinyl acetate, ethyl acrylate or acrylic acid, and the surface of which exhibits a wet tension not smaller than 36 dyne/cm.
Japanese Unexamined Utility Model Publication (Jikkai-sho) No. 61-50437 discloses a film for print lamination which comprises a biaxially drawn polypropylene film having a heat-adhesive layer provided on one side thereof, said heat-adhesive layer comprising a copolymer of ethylene and acrylic acid, acrylic ester, methacrylic acid or methacrylic ester.
Japanese Unexamined Utility Model Publication (Jikkai-sho) No. 62-126931 discloses a film for print lamination which comprises a first layer comprising a biaxially drawn polypropylene film, a second layer comprising a polyolefin film, and a third layer, as a heat-adhesive layer, which comprises an ethylene propylene block copolymer, a petroleum resin and an ethylene acrylic acid copolymer.
A heat/pressure bond type print lamination film is inferior in slipperiness and antiblocking characteristic. In consequence, troubles are experienced such as wrinkling during production of the film and deterioration of the flatness of the film surface or a breakage of film due to adjacent film surfaces sticking to one another when being unwound from a roll.
In order to obviate these problems, it has been proposed to add a large quantity of polymer having poor compatibility, organic lubricant and inorganic particles so as to impart a high slipperiness and antiblocking characteristic. The use of such additives causes other problems such as degradation in the heat-adhesiveness, inferior quality of the print laminated product such as the occurrence of many voids and fisheyes in the bonded layer. In addition, this type of film exhibits inferior flexing resistance so that defects such as local separation or floating of the film from the printed paper are experienced when the laminate product is bent after the heat bonding.